Forbes ranked Prince Alwaleed, 58, as number 26 on their annual list released in March, with a net worth of $A21.21 billion (US$20 billion.)

But the Prince claims his actual fortune is closer to A$31.18 billion (US$30 billion) and slammed the magazine for being biased against wealth from the Middle East, The Guardian UK reports.

He has launched a defamation case against Forbes, the editor and two journalists in London's High Court.

Prince Alwaleed describes himself as the "world's foremost value investor" and holds large stakes in luxury hotels around the world including the Four Seasons, The Savoy in London and the George V in Paris.

He also owns shares in News Corporation, Citigroup, Apple and Twitter through his investment company Kingdom Holding which is listed on the Saudi exchange, and has a lavish personal lifestyle including a gold throne in his private jet.

Forbes released a statement saying they stand by their original story, having calculated his net worth based on the underlying value of his investments, rather than the price of stocks on the Saudi Arabian exchange.

The company also said they have been subject to lobbying and threatening from Prince Alwaleed's advisers in an attempt to boost his ranking on the list, according to The Guardian UK.

To win the case, the Prince will have to prove he suffered serious harm and financial loss as a result of the article.

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